The relation between inter planer spacing(d), lattice parameter and miller indices (hkl)

A. $$n\lambda d = \frac{a}{{\sqrt {{h^2} + {k^2} + {l^2}} }}$$

B. $$\lambda = \frac{d}{{a\sqrt {{h^2} + {k^2} + {l^2}} }}$$

C. $$d = \frac{a}{{\sqrt {{h^2} + {k^2} + {l^2}} }}$$

D. None of these

Answer: Option C